I think I see what you are asking and honest? I don't think it works. I have had people come far and wide from 5 hrs away and it never tells me what they have. It doesn't suddenly update when it gets in range of my beacon tower so if they are attacking outside the cone, they get to come in unchecked.

What is the range based on level? I'm not sure. Or if that's even a factor and it isnt something to do with the attacking hero's Intell and informatics. It never mattered to me anyway. All I need to know is what city they plan to hit. Knowing they have 200K warriors or 200K Ballista won't change my abilty to beat them or not.